The present invention relates to an optical integrated circuit element. More particularly, the present invention relates to an optical integrated circuit element having an optical waveguide which includes integrally as a portion thereof a region containing an isoelectronic impurity, in which region an optical amplification and/or laser function are performed.
It is well known that there sometimes arises the necessity of using a portion of an optical waveguide as an optical amplifier or laser as, for example, in the case of a repeater in an optical communication system. In general, optical amplification is realized by first causing an inversion in the electron and hole population of a material and then introducing the material with an incident light having energy nearly equal to the forbidden band gap of the material to stimulate recombination of electrons and holes and generate light having the same wavelength and phase as the incident light. However, when this principle is applied to an optical element, the amplification region is formed in a portion of the waveguide and as a result, the amplification effect is greatly reduced due to the large absorption loss in the waveguide when the waveguide region and the amplification region are made of the same material. Further, in order to use a portion of the waveguide as a laser, it has been proposed to use a distributed Bragg reflector type semiconductor laser which has a reflector on opposite sides of the amplification region of the waveguide formed by providing periodical corrugation, the pitch of which is a half integer times the oscillation wavelength. This is because, when a laser is required to be contained as a portion of a monolithic optical integrated circuit, it is impossible to use the cleavage plane which has been used as the reflector. Also in this case, when the Bragg reflection region is made of the same material as that of the waveguide, the re-absorption of the light output generated in the Bragg reflection region is large in the optical waveguide and, therefore, the efficiency thereof as a whole becomes low. In order to avoid this disadvantage, it is usual to made the Bragg reflection region with a material which exhibits lesser absorption or to taper the waveguide to guide the light to a layer of low absorption. The above methods of avoiding the above mentioned disadvantage require a complicated waveguide structure, causing an increase in fabricating processes and hence an increase in cost.
An object of the present invention is to provide an optical circuit element which is easily formed integrally with an optical waveguide and which works as an amplifier and a laser and couples with waveguide region with high efficiency.